The invention relates to a hybrid drive system for a motor vehicle, which hybrid drive system contains an internal-combustion engine, a generator, an electric motor, an electric energy accumulator coupled with the generator and the electric motor by way of a controllable converter device for controlling the electric energy flow, a connection device for establishing mechanical couplings between the internal-combustion engine, the generator, the electric motor and the vehicle, and a control device for controlling the converter device and the connection device as a function of the charge state of the energy accumulator and the drive power demand of the vehicle.
Because of the increasing importance of an improved environmental compatibility of motor vehicles, hybrid drive systems of the above-mentioned type are becoming more significant. They permit the avoidance of an operation of the internal-combustion engine in ranges with a particularly high specific fuel consumption. Such operating ranges are connected with high, route-related fuel consumption of the vehicle as well as with high emission of pollutants.
Hybrid drive systems of the above-mentioned type are known, for example, from German Patent document DE 29 43 554 A1, Japanese Laid-Open Utility Model 2-7702, International Patent document WO 00/15455 and U.S. Pat. No. 5,934,395.
It is an object of the invention to further develop a hybrid drive system of the above-mentioned type such that its environmental compatibility is improved.
Solutions of this object are achieved according to the invention. By designing the hybrid drive system according to an aspect of the invention, it is ensured that, when the battery is full, the internal-combustion engine is used for driving the vehicle only if, when driving the vehicle, it runs at an operating point having a specific fuel consumption which is less than the effective specific fuel consumption which occurs when the vehicle is driven electromotively, and it is taken into account how the energy accumulator was charged.
By means of the hybrid drive system according to another aspect of the invention, it is ensured that the vehicle will be driven by the electric motor only when the respective driving power cannot be provided more economically by the internal-combustion engine.
In accordance with further aspects of the invention, it is ensured that the electric energy accumulator is recharged with the best possible effective specific fuel consumption.
Further advantageous embodiments and further developments of the hybrid drive systems according to the invention are described and claimed herein.
In accordance with still further aspects of the invention, it is ensured that, in each case, the recharging of the electric energy accumulator always takes place with the lowest possible fuel consumption of the internal-combustion engine.
Additionally, the basic design of the control device is such that the vehicle can always be driven with the lowest possible effective fuel consumption.
It can be ensured by means of other aspects of the invention that the energy accumulator always contains a sufficiently large energy reserve which at least makes possible a reliable starting of the internal-combustion engine from the energy accumulator.
In accordance with another aspect of the invention, it is achieved that, in certain operating conditions, for example, when the electric energy accumulator is still substantially full, a recharging will take place only when the energy, which will be additionally stored in the energy accumulator, will be generated with a better efficiency than the energy still present in the energy accumulator.
In accordance with another aspect of the invention, it is achieved that the operating behavior of the hybrid system can be adapted to a predetermined, repeatedly traveled route such that this route will be traveled with minimal fuel consumption.
Further aspects of the invention are aimed at the advantageous dimensioning of components of the hybrid drive system, at possibilities of starting the internal-combustion engine in the case of a particularly simple embodiment of a hybrid drive system, and at a particularly advantageous and simple embodiment of the hybrid drive system.
Advantageously, a two-cycle internal-combustion engine can be used in a hybrid drive system according to the invention because operation of the internal-combustion engine can be avoided in operating ranges in which the two-cycle method presents problems.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.